Hollow piston



May 19, 1931. Y A, STEPHENS 1,8051958 HLLow PIsToN Filed Nov. 23, 1926 Patented May 19, 1931 UNlTED STAT-ES ARNOLD A. STEPHENS, 0F DAVENPORT, IOWA HOLLOW PISTON Application led November 23, 1926. Serial No. 150,307.

This invention relates to engine pistons and more particularly to pistons of non-ferrous metals or alloys.

It has been proposed heretofore to construct pistons of aluminum. The relative light Weight o this metal makes it desirable for such a use. Such pistons, however, have not given satisfactory service. Due to its high coellicient of thermal expansion, it was necessary to allow a relatively large initial clearance between the piston and the cylinder bore. Decided disadvantages resulted from this, such as accentuated piston slap and excessive cylinder wall wear.

To improve. the elliciency of such aluminous pistons it was suggested to make the skirt of a relatively large diameter and to provide it with splits, so that the whole skirt could compress as the material expanded due to the hi h temperatures obtaining Within the cylin er.

In the ordinary constructions of pistons embodying this feature, the skirt is cut away at that portion betvveen the oil ring and wrist pin bosses. The use of this design of piston is attended by serious disavantages. The cut away portion causes a break in the heat couducting path from the head to the skirt and concentrates heat at the bearings, thereby causing distortion on these stressed parts. In addition, this eut away portion lowers the actual bearing surface of the piston which results in vibration of the piston head and consequent heavy Wear.

It is an object of my invention to provide a piston of light weight in which lateral motion is reduced to a minimum.

Another object is to provide a piston which has a high hearing surface.

A further object is to provide a piston which dissipates heat effectively Yet another object is to provide a piston of a light metallic material of simplified structure which may operate with a minimum of clearance.

I accomplish the. foregoing and other ini portant and related objects by constructing a piston of a metal or metallic alloy of low speciic gravity and having a rigid head and compressible skirt and fitted with a high bearing section preferably of a metal of a higher specific gravity than the metal of the piston proper.

To make my invention more clearly understood I have shown in the accompanying drawings a practical embodiment which comprehends its salient features and in which like reference numerals refer to similar parts throughout the several figures, of which,

Figure l is a side elevation of the piston mounted in a cylinder;

Fig. 2 is an elevation taken at a right angle to the vien7 of Fig. l;

Fig. 3 is a section on the line 3 3 of Fig. 2;

Fig. 4 is a detail View of a portion of the device shown in Fig.

Tn Fig. l there is shown a cylinder 1 enclosed by a iva'ter jaelteted engine block 2 and cylinder head it. Within the cylinder there is mounted a piston 4. rllhe piston is connected to an engine shaft through the intermcdiacy of a connecting rod 5. Wrist pin 6 and Wrist pin bushings i' in the conventional manner.

The piston may he composed of a metal or metallic alloy having a low specific gravity as compared to iron. l prefer to construct the piston ot a line grained aluininous material, either aluminum or an alloy of aluminum having the requisite strength for this use.

The piston comprises a head portion 4 and a skirt section 5. The head is truly circular and is provided With a plurality of grooves. One group ol grooves maybe ofthe same size to receive the piston rings 8 and 9 and the oil ring l0. 'The other groove l1, shown particularly in Fig. il, is of much greater height than the compression ring grooves and is adapted to seat a hearing member 12, to be more fully described hereinafter.

The skirt portion as initially formed comprises a plurality of integral cylin-'lrical se*- tions. On the thrust side of the piston the skirt is formed with a quadrantal cylindrical section 13 which has a greater radius than the remaining cylindrical section, as described in my copending application Serial No. 101,940. At the side opposite the thrust side the skirt is split as at 14. As shown, particularly in Fig. Q, this is a Y-shaped cleft although it is to be understood that I may use a single or any desired type of split.

It will now be seen that the lower portion of the skirt` and more especially that section subtended by the V-shaped split 15 and adjacent the vertical split 14 will tend to spring out or expand. These portions will bear against the c vlinder bore and serve to restrict lateral movement of the lower part ofthe piston. As the piston becomes heated, this aluminous material will expand considerably because of its relatively high thermal expansion. liy constructing the piston as described there is provided, in etiect. an expansible and contractible skirt. In the early running stages, when the piston is relatively cool, the expanded lower section of the skirt presents too great a clearance between the cylinder and piston. As the piston becomes heated the lower part of the skirt will expand and tend to press against the cylinder bore. Should the skirt expand beyond the minimum clearance the ends adjacent the vertical split will approach each other, due to pressure exerted by the cylinder wall. Thus the danger of seizing iseliminated.

As intimated herenbefore, in the usual aluminum piston construction the skirt is cut away for a portion of its length between the wrist pin bosses and the oil ring. In addition to causing distortion of the wrist pin bosses and allowin vibration of the piston head, this method o construction weakens an aluminum piston considerably.

I find that these undesirable effects can be obviated by providing a separate bearing surface in the piston head. I accomplish this by placing in the head an annular Section of metal of a coetiicient of expansion a proxiniating that of the metal of the cylin er.

As shown in Fig. 3, this auxiliary head section comprises an annular split ring l2. Because of its cheapness and its thermal expansion cocflicient, I prefer to use iron. This member, while carried by the head, is contractible independently of the head. Positioned intermediate the ring and the bottom of its cooperating groove is a polygonal spring 1V. rlhis resilient member conforms in circuinl'erential length to that of the seetion of that skirt of smaller diameter. Seated in the groove between the free ends of the spring is a filler block 17. The ring 12 is maintained in circular form by the cooperating action of the spring and tiller block.

To prevent unrestricted action ot' the spring, I have provided a means for limiting its expansion. This comprises a supporting base 18 which is of the same curvature as the groove bottom and filler block. Integrally formed with the supporting base and intermediate its ends is a tenon 19. On its other side, at each end` the base is formed with integral extending undercut pins 20. These pins are adapted to register with the channels 21 cut in the interior periphery of the ring. It will be noted that the channels are considerably wider than the locking pins and hence the ring may expand and contract through a limited range. It is to be understood that the filler block is of appropriately reduced width at that portion which abuts the plate 19. The tenon 19 is seated in a recess in the filler block. This effectively anchors the plate 18 and tillcr block against circumferential movement in the groove. While I have shown the filler block and locking plate as separate pieces. it will be appreciated that I may provide ring locking pins on the filler block itself and anchor this to the piston by any suitable means.

The operation of the bearing ring will be apparent from the foregoing description. The spring 16 will tend to expand the ring to the limit allowed by the locking means, that is until the edges of the undercut pins abut the sides of the channel adjacent the angular split. The spring forces the ring away towards the side opposite the thrust side and hence maintains the ring in close ontact with the filler block and supporting ase.

When the piston is inserted in the cylinder bore, th ring may bear against the adjacent cylinder wall. As it is run in, a glazed surface is worn on the ring and a small clearance between the ring and cylinder is insured. It will now be appreciated that the piston head is in effect that of cast iron in respect of cylinder clearance. Due to the provision of the resilient member and allowance of movement of the bearing ring the aluminous material of the head may expand or contract independently of the auxiliary iron head section. The contractibility of the ring preeludes the possibility of seizing, since this member can exert a pressure against the cylinder bore only equal to the expansive force of the spring.

By providing a high bearing surface in conjunction with a contractible skirt portion,

bodily lateral movement and oscillation about the wrist pin is minimized. This structure in addition enables the construction of a full cylindrical piston and this insures the maximum strength.

A piston constructed in accordance with this designdissipates heat generated in the cylinder head most effectively. A continuous heat conducting path from the head to the skirt is provided. This, as has been pointed lni out, prevents concentration of heat at the wrist pin bosses and thus eliminates the danger of distortion of these parts. This piston combines the advantages of the light weight of aluminum with the desirable clearance features of cast iron. The device is of simple construction comprising but few easily assembled and replaceable parts.

While I have shown and described a preferred embodiment of the invention, it is to be understood that this is given but as an example of one way in which the underlying features of the invention may be incorporated in a mechanical structure, for since the invention is susceptible of other mechanical embodiments, I do not intend to be restricted to any particular structure except as such limitations are imposed in the appended claims.

I claim:

l. A hollow piston comprising a rigid head and resilient skirt portion, a split contractible and expansible bearing member in the head having less thermal expansion than the material of the piston and means to limit the expansion of the bearing member.

2. A hollow piston comprising a rigid head and a resilent skirt portion, a separate substantially freely contractible and expansible section in the head of a different material from that of the head and skirt expansible and contractible independently of the head.

3. A hollow piston comprising a head and split skirt portion of a metal having a relatively low specific gravity, compression rings in the head, a separate substantially freely expansible and contractible head section of a metal of a lower degree of thermal expansion than the metal of the head and skirt and means cooperating with the head and the head section to limit the expansion of the head section.

4. A piston of the character described comprising a rigid head provided with compression rings, a full cylindrical split skirt integrally formed with the head, the head and skirt being formed of a metal of relatively low specific gravity, a separate split head section of a material having a lower degree of thermal expansion than the metal of the head and skirt and means to limit the expansion of the head section.

5. A piston of the character described comprising a head and a split skirt forming a continuous cylindrical surface with the head. the head and skirt being formed of a material of relatively loiv specific gravity and relatively high degree of thermal expansion, a yseparate annular section mounted in the head expansible and substantially freely contraciible indeliendently of the head. said section being formed of a material of greater specific ygravity and of smaller degree of thermal Ve-xpansion than the metal of the head and skirt.

(l. A piston comprising a head and resilient skirt of an aluminous material, compression rings carried by the head, a separate annular head section of ferruginous material expansible an contractible independently of the head and means cooperating with the head and said section to limit the expansion of the latter.

7. A piston comprising a head and skirt of aluininous material, compression rings carried by the head, a separate annular head section of a ferruginous material provided with means to limit its expansion and permit sul stantially free construction. the skirt section being split at one side and at the opposite side being formed with an extended segment.

8. A piston comprising a head and resilient skirt of au aluminous material, compression rings carried by the head, a separate annular expansible head section 0f a ferruginous material and means to limit the expansion and permit substantially free contraction of said section including under cut pins supported by the head and engaging the section.

9. A piston comprising a rigid head and a split skirt of a metal having a relatively low specific gravity, a spaced head section expansible and substantially freely contractible independently of the piston head and of a material having a greater specific gravity than the piston, means carried by the head to limit the expansion of the section.

l0. A piston comprising a head and skirt of a material having a specific gravity less than iron, a separate annular expansible section of ferruginous material mounted in the head, and means to restrain the expansion of the section comprising a curved plate having oppositely projecting members adapted to secure the plate to the piston and to restrain the expansion of the section.

l1. A restraining means of the character described comprising a plate having oppositely projecting central and end extensions.

l2. A piston comprising a body portion of a material having a specific gravity less thanv iron, a separate annular radially expansible section formed with grooves in its interior face, and means detachably secured to the piston body and slidably engaging the grooves to restrain expansion of the section.

13. A piston comprising a head provided with compression rings, a skirt, an expansible annular section mounted in a groove in the piston, means detachably seated in the groove to limit the expansion of the section and to transmit the thrust of the piston directly to the' section.

14. A piston comprising a body portion ot an aluminous material, a .separate annular expansible section maintained in the pistou` aud means to limit the expansion of the section comprising a single piece of metal having .spaced angularly projecting arms and engaging the section to limit its expansion. and a second oppositely extending projecticn for connection with the piston body.

15. A piston having a head and skirt, a plurality of compression rings and an oil ring` carried in grooves in the head, a split bearing ring of greater width than the com- 5 pression rings supported in a groove positioned above the oil ring, a resilient member interposed between the bearingring andthe bottom of its cooperating groove, and means coacting with the bearing ring adjacent `the u, Split thereof to limit the expansion of said bearing ring.

In testimony whereof I aix m si nature.

ARNOLD A. STEyPI-IgENS. 

